Männiste Marju, Hõrak Peeter
Department of Zoology, Institute of Ecology and Earth Sciences, Tartu University, Tartu, Estonia.
J Exp Zool A Ecol Genet Physiol. 2011 Nov 1;315(9):527-35. doi: 10.1002/jez.701. Epub 2011 Sep 6.
Elevation of glucocorticoid (GC) hormone levels is an integral part of stress response (as well as its termination) and immunomodulation. These hormones are also responsible for mobilizing energy stores by stimulation of gluconeogenesis and inhibition of protein synthesis. Elevation of GCs is thus incompatible with other protein-demanding processes, such as moult. Previous studies have shown that chronic elevation of GC hormones suppresses feather growth. Here, we asked whether similar effect would also occur in the case of acute GC elevation and induction of an inflammatory response by foreign antigen. We performed an experiment on captive wild-caught greenfinches (Carduelis chloris) injecting birds with phytohaemagglutinin (PHA) and dexamethasone (DEX) in a factorial design. To assess the possible somatic impacts of these manipulations, we removed one of the outermost tail feathers before the experiment and measured mass and rachis diameter and length of the replacement feathers grown in captivity. Immunostimulation by PHA reduced rachis length, but did not affect feather mass or rachis diameter. Single injection of a synthetic GC hormone DEX significantly reduced all three parameters of feather size. Altogether, these findings demonstrate the sensitivity of feather growth to manipulation of immune and adrenal functions. Our results corroborate the somatic costs of immune activation and suggest that even a short-term elevation of GC hormones may induce long-term somatic costs with a potential impact on fitness. Our findings also imply that a single injection of DEX, frequently used as a diagnostic tool, can have lasting effects and researchers must consider this when designing experiments.
糖皮质激素（GC）水平的升高是应激反应（及其终止）和免疫调节的一个组成部分。这些激素还通过刺激糖异生和抑制蛋白质合成来调动能量储备。因此，GC水平的升高与其他需要蛋白质的过程（如换羽）不相容。先前的研究表明，GC激素的长期升高会抑制羽毛生长。在这里，我们探讨了在急性GC升高以及外源抗原诱导炎症反应的情况下是否也会出现类似的效果。我们对圈养的野生绿雀（绿雀属）进行了一项实验，采用析因设计给鸟类注射植物血凝素（PHA）和地塞米松（DEX）。为了评估这些操作可能对身体产生的影响，我们在实验前拔掉了最外侧的一根尾羽，并测量了圈养环境中生长的替换羽毛的质量、羽轴直径和长度。PHA免疫刺激减少了羽轴长度，但不影响羽毛质量或羽轴直径。单次注射合成GC激素DEX显著降低了羽毛大小的所有三个参数。总之，这些发现证明了羽毛生长对免疫和肾上腺功能操作的敏感性。我们的结果证实了免疫激活的身体成本，并表明即使GC激素的短期升高也可能导致长期的身体成本，对健康产生潜在影响。我们的发现还意味着，经常用作诊断工具的单次DEX注射可能会产生持久影响，研究人员在设计实验时必须考虑到这一点。
